1. Field of Invention
This invention relates to improvements in methods and apparatuses for dynamic information storage or retrieval, and more particularly to improvements in methods and circuitry for detection of synchronization servo marks (SSMs), especially in information storage and retrieval systems that use a magnetic data storage medium.
2. Relevant Background
Mass data storage devices include tape drives, as well as hard disk drives that have one or more spinning magnetic disks or platters onto which data is recorded for storage and subsequent retrieval. Hard disk drives may be used in many applications, including personal computers, set top boxes, video and television applications, audio applications, or some mix thereof. Applications for hard disk drives are still being developed.
Mass data storage devices may also include optical disks in which the optical properties of a spinning disk are locally varied to provide a reflectivity gradient that can be detected by a laser transducer head, or the like. Optical disks may be used, for example, to contain data, music, or other information.
Typically in a hard disk drive, for example, a rotating storage disk may be formed of a suitable substrate material such as metal or glass onto which a thin film magnetic storage medium may be vacuum sputter deposited onto the disk. The disk has a central opening to enable a rotating hub to securely clamp the disk to a disk spindle. Synchronization servo data is imprinted by altering the magnetic domains on the disk in each sector of each track of the disk, usually following servo burst recorded thereon for head alignment along the track. As the head travels along the path of the track with which it is currently aligned, electrical signals are induced into the head by the magnetic flux recorded on the spinning disk. The electrical signals can then be processed in the read channel of the device to determine the instantaneous position of the head. One of the signals recorded onto the disk is a synchronization mark from which timing and other data retrieval activities can be based which must be detected before any such data retrieval activities can be commenced.
In the past, conventional synchronization servo mark (SSM) detection schemes detect a data stream from the head. The data stream contains the SSM, which must be identified. Previously, this was done by directly comparing the data stream to the known synchronization pattern to determine the number of bit matches and mismatches. If the value of the mismatched bits is less than a programmed error tolerance, the synchronization pattern is considered to have been found at that point.
Typically, the detection electronics of a hard disk drive is synchronous, and until the synchronization mark has been properly detected, some phase error may exist between the circuit clock and the synchronization servo mark. When the phase error is small enough, such pattern matching detection schemes show good performance. However, when the phase error is large (0.25 Tc), the detector cannot detect the synchronization mark data stream correctly. The use of a d=1 constraint synchronization mark pattern improves the phase immunity, but an ideal detector cannot recover the synchronization mark pattern correctly when a phase error approaching 0.5 Tc exists. Any delay that is experienced in the detection of the synchronization mark results in a decrease in system speed, which is undesirable.
What is needed is a method and detector for detecting the synchronization mark in a mass data storage device, or the like, that has a wider tolerance for such phase error so that the synchronization mark can be more rapidly and accurately detected.
In light of the above, therefore, it is an object of the invention to provide a method and detector for detecting the synchronization mark in a mass data storage device, or the like, that has a wider tolerance for such phase error so that the synchronization mark can be more rapidly and accurately detected.
One aspect of the invention derives from the notion that the synchronization servo mark (SSM) pattern itself does not need to be recovered correctly. The significant information is only the location of the SSM pattern. The SSM detector of the invention uses a single matched filter for detection of SSM location. The SSM pattern and the matched filter have been designed such as the output of the matched filter has the maximum value at the proper SSM location and has sufficiently small values at any other locations to avoid false synchronizations. The SSM can be detected by knowing the location with the maximum value of the matched filter output in the SSM detection window.
Thus, according to a broad aspect of the invention, a detector is presented for detecting the location of a synchronization mark in a data stream read from a recording medium of a mass data storage device. A matched filter is arranged to receive selected bit combinations of a received data sequence containing the synchronization mark shifting thereby, the matched filter being constructed to produce an output value that is of maximum magnitude when the synchronization mark has just shifted thereby in a next preceding time interval. A xe2x80x9cDxe2x80x9d element receives the output value from the matched filter to produce a xe2x80x9cDxe2x80x9d element output. When the xe2x80x9cDxe2x80x9d element output is greater or equal to a predetermined threshold value and is larger than the output value, the synchronization mark is in a current time location, and when the xe2x80x9cDxe2x80x9d element output is greater or equal to the predetermined threshold value and is less than or equal to the output value, the synchronization mark is in a next time location. The predetermined threshold value may be established to be less than the maximum magnitude if a phase of the synchronization mark is within a predetermined phase range.
The matched filter is matched to a corresponding synchronization servo mark, which is selected to produce the best signal-to-noise ratio with respect to the rest of the data that is contained in the data stream in which the synchronization servo mark is searched. In one embodiment, the synchronization servo mark is 30 bits long, and may be NRZI xe2x80x9c101010001010101000101000100010xe2x80x9d.
According to another broad aspect of the invention, a detector is presented for detecting the occurrence of a synchronization mark in a data stream. The detector includes an input data delay element through which detected data containing the synchronization mark is clocked and an adder for receiving the data containing the synchronization mark and an output of the input data delay element to produce a summed output representing a sum of two consecutive data bits in the data stream. The summed output is successively clocked through a chain of data delay elements having a length of two less than a length of the synchronization mark. A filter is connected to receive at least some of the data from the chain of data delay elements the filter producing an output data stream. An output delay element receives the output data stream, and a first comparator compares an output of the delay element to a predetermined threshold value to produce a predetermined output state when the output of the output delay element is larger than the predetermined threshold value. A second comparator may be provided for comparing the output data stream to the output of the output delay element to produce a first predetermined output state when the output data stream is larger than the output of the output delay element and a second predetermined output state when the output data stream is smaller than the output of the output delay element.
According to yet another broad aspect of the invention, a method is presented for detecting the location of a synchronization mark in a data stream read from a recording medium of a mass data storage device. The method includes applying selected bit combinations of a shifting received data sequence containing the synchronization mark to a matched filter that produces an output value that is of maximum magnitude when the synchronization mark has just shifted thereby. The output value is delayed for one time period to produce a delayed value. Thus, when the delayed value is greater or equal to a predetermined threshold value and is larger than the output value, the synchronization mark is in a current time location. When the delayed value is greater or equal to the predetermined threshold value and is less than or equal to the output value, the synchronization mark is in a next time location.
According to yet another broad aspect of the invention, a mass data storage device is presented. The mass data storage device includes a data medium containing a synchronization mark contained thereon and a data transducer arranged to read data from the data medium, including the synchronization mark, to produce a data stream. A matched filter is arranged to receive selected bit combinations of the data stream, the matched filter being constructed to produce an output value that is of maximum magnitude when the synchronization mark has just shifted thereby in a next preceding time interval, and a xe2x80x9cDxe2x80x9d element for receiving the output value from the matched filter to produce a xe2x80x9cDxe2x80x9d element output. When the xe2x80x9cDxe2x80x9d element output is greater or equal to a predetermined threshold value and is larger than the output value, the synchronization mark is in a current time location. When the xe2x80x9cDxe2x80x9d element output is greater or equal to the predetermined threshold value and is less than or equal to the output value, the synchronization mark is in a next time location.
According to yet another broad aspect of the invention, a detector is presented for detecting the occurrence of a synchronization mark in a data stream. The detector includes a chain of data holding elements having a length as long as the synchronization mark and through which detected data containing the synchronization mark is successively clocked and a filter connected to receive at least some of the data in the data stream from the holding elements. The filter is configured to produce a maximum output when a desired synchronization mark is contained in the chain. A comparator receives the output to produce an output state when the sum is larger than a predetermined threshold value. The predetermined threshold value may be established to be less than the maximum sum if a phase of the synchronization mark is within a predetermined phase range.